Judging by what my Google search turn up, phrases like
"Keeper of your/my/his conscience" tend to be third parties.
One of the more famous examples is Gandi who said that
Chakravarthi Rajagopalachari was "the keeper of my conscience"

On the other hand "voice of my conscience," the more common expression, usually refers to something internal to the individual.

I hear voices all the time, most often when I forget my meds. But I don't know if any one of them is the voice of my conscience because they all speak in languages I don't understand, except for maybe a word here and there.